Ovalidota milleri, Pawson, David L., 2004

Pawson, David L., 2004, Ovalidota milleri, a new genus and species of bathyal sea cucumber from the Caribbean Sea (Echinodermata: Holothuroidea: Apodida), Zootaxa 561, pp. 1-6 : 3-5

Ovalidota milleri new species

Figures 1–2

Diagnosis: Body approximately 22 mm long. Body wall translucent, color in life greyishwhite to light violet; in alcohol light brown.

Material Examined: HOLOTYPE, Catalogue No. HBOM 071:00505, Harbor Branch Oceanographic Museum, 5600 U.S. 1 North, Fort Pierce, Florida 34946. R/V Seward Johnson, Johnson­Sea­Link II Dive 1747, York Bay, off York Point, St. Vincent, Lesser Antilles, 13°07.2'N, 61°16.8'W, 25 April 1989, 413.9 meters, 1 specimen, collected along with sediment by a suction device. Total length 21.5 mm. Collected by J. E. Miller.

Other material: Photograph ( Figure 1 , top) of live specimen in situ on wall at Grand Cayman Island, depth 1,200 feet. Photograph taken from a manned submersible by Gary Montemayor. Total length approximately 22 mm (calculated by comparison of size of wheel papillae with those of Holotype).

Description: Holotype in poor condition, flattened, elongate oval, 21.5 mm long, 12.5 mm wide at widest point, near anterior end (width:length = 1:1.72). Recently­dead Holotype, when photographed ( Figure 1 , bottom left, bottom right), with same body proportions. Photograph of live specimen at Grand Cayman ( Figure 1 , top) shows that body is more or less egg­shaped, approximately twice as long as wide. Dorsal surface strongly arched; shape of ventral surface unknown, probably arched also. Mouth, ventral, lying approximately 5.5 mm from anterior end of body, in life facing substratum. Oral field extensive, circular, approximately 7 mm in diameter, bounded by 18 or 19 large tentacles, each approximately 2.3 mm in diameter when retracted. In live specimen, extensile tentacles approximately 5.5 mm long, transparent and cylindrical when extended into the substrate in the feeding mode. Tentacles appear to have terminal discs bearing a fringe of digits ( Figure 1 , bottom left); their detailed morphology cannot be determined. Anus terminal.

Body wall translucent, color light violet in the laboratory, grayish in life. Radial muscle and intestine visible through body wall. Conspicuous on body wall are numerous wheel papillae ranging up to approximately 1.1mm in diameter, each consisting of loosely aggregated heaps of wheel ossicles. Individual wheels also scattered in body wall between papillae. Wheel papillae scattered in radii and interradii, more numerous dorsally than laterally or ventrally. Largest papillae in anterodorsal region of body. Internal anatomy not examined. A substantial calcareous ring is present, visible through the body wall ( Figure 1 ); the intestine appears to describe the typical loop in its path from mouth to anus.

Body wall ossicles exclusively wheels ( Figure 2 ), scattered in the body wall and gathered into heaps in wheel papillae. Wheels severely corroded, apparently due to slightly acid nature of preservative. Wheels apparently typically chiridotid, with six spokes (Figure 2A) and with a central “star” pattern as described by Smirnov (1998). Rim of wheel with typical chiridotid teeth ( Figure 2 B, 2C); fragment of wheel with remains of teeth on rim allows estimate of approximately 150 teeth per average wheel. Wheel diameter range 211–267µm, standard deviation — n­1 is 18.70 (n=10, mean 237µm). Tentacles with smooth rods with few lateral projections and slightly branched ends; average length of rods 100µm.

Ecological notes: The Holotype was collected along with soft sediments, and the photographed specimen from Grand Cayman was apparently feeding on a soft substratum. The ventrally­directed mouth appears to equip the animal for obligate feeding on the substratum, rather than feeding on a mixture of detrital and suspended material that seems to be an option for other deep­sea chiridotids ( Pawson & Vance, 2004; Smirnov et al., 2000).

Remarks: The color of this species may be variable and, because the animal is translucent, the color in situ may also reflect the nature of the substrate to a considerable extent. In terms of general appearance, number of spokes, central “star” pattern, the wheels of this species appear to be typically chiridotid. The wheels are distinctive in being very large, and in having numerous teeth on the rim, but these characteristics fall within the range of variation in the Chiridotidae ( Clark, 1908) .

Figures

FIGURE 1. Ovalidota milleri new genus, new species. Top, live specimen, in situ, on The Wall at Grand Cayman Island, depth 1,500 feet. Photograph: Paul Montemayor. Lower left, Holotype, total length 22 mm, ventral view. Photograph: J. E. Miller. Lower right, Holotype, dorsal view. Photograph J. E. Miller.

FIGURE 2. Ovalidota milleri new genus, new species. A. Wheel ossicle, somewhat corroded. B. Scanning electrom microscope image of portion of corroded wheel ossicle, showing remains of teeth on inner margin of rim. C. Photograph of portion of corroded wheel ossicle. Note evidence of teeth where spokes meet the wheel rim.